All kinds of PC security authentication methods in prior art are once-authentication, i.e. the PC client only needs to send a registry request to a Server while the PC client logging in, once the user identifier such as ID number and password passes authentication made by the Server, said PC will be able to access the services legally, which means the Server will no longer identify the PC client is legal or not when the PC utilizes the services.
The once-authentication method in prior art may give chances to illegal PC users to embezzle legal accounts. The FIG. 1 shows a flow graph of PC client authentication and utilization in a more typical ICW (Internet Call Waiting) service, wherein, Internet personal number (IPN) represents ID number such as account number or other various service numbers which can identify a subscriber. As shown in the drawings, if a legal subscriber has succeeded in the PC registry authentication, a wiser illegal PC subscriber can overleap the step of PC registry authentication, and use the number directly to initiate calls, occupying charge and resources of the legal subscriber.